Tube bending mandrel



y 15, 1969 c. H. l QOERTS I 3,455,142

. TUBE BENDING MANDREL Filed Aug. 12, 1965 INVENTOR.

CHARLES H. ROBERTS A TTQRNE Y United States atent O 3,455,142 TUBE BENDING MANDREL Charles H. Roberts, Sun Valley, Calif., assignor to Tools for Bending, Inc., Denver, Colo., a corporation of Colorado Filed Aug. 12, 1965, Ser. No. 479,232 Int. Cl. Bllb 25/00 US. Cl. 72-466 Claims ABSTRACT OF THE DISCLOSURE A universal tube-bending mandrel has flexible mandrel sections comprising ball and socket connecting links of one-piece construction where each ball is retained in the socket of each next connecting link by means of a split locking member inserted behind the ball portion in such a way as to substantially eliminate end play or axial shifting between the interconnected links while permitting complete freedom of pivotal and rotative movement therebet-ween.

This invention generally relates to tube bending mandrels; and more particularly relates to a novel and improved mandrel or tool which is adaptable for insertion within a tube along the section to be bent and which upon bending will internally support the tube to prevent flattening or collapse in a dependable and eflicient manner.

In tube or pipe bending operations, it is customary to employ a mandrel which will fit within the tube along the length of the tubular section to be bent to afford the necessary internal support in order to prevent reduction in size or collapse of the tube in bending. In conventional practice the mandrel is universally flexible and at least the flexible section of the mandrel is variable in length by adding or subtracting sections or links depending upon the length of the tubular section to be bent. For example, typical mandrels of this type are set forth and described in the patents to H. B. Condifl 2,962,077 and to H. M. Spates 3,190,106.

In accordance with the present invention it is proposed to greatly facilitate the tube or pipe bending operation by devising an improved flexible mandrel construction which assures the necessary flexibility and internal support for the tube under bending, and also incorporates improved means of connection and disconnection between the flexible mandrel sections; and further, once assembled eliminates any end play between the sections so as to be of consistent length and obviate the use of spring-loaded or resilient elements between the sections. Moreover, spacing between the flexible sections is held at a minimum without in any way restricting the flexibility of the sections.

Accordingly, it is an object of the present invention to provide for an improved flexible mandrel for use in tube and pipe bending operations wherein the mandrel has flexible mandrel sections variable in length and easily assembled and disassembled while providing for positive interlocking connection therebetween.

It is another object of the present invention to provide for more positive but releasable locking between flexible mandrel sections in a tube bending mandrel and in such a way as to substantially eliminate end play or axial shifting therebetween; and further wherein the entire assembly is extremely durable and long-lasting in use with smooth flexing about a common center line radius between the flexible sections.

It is a further object of the present invention to provide, in a universal tube bending mandrel of the ball and socket type, for the novel placement and arrangement of locking members behind the ball portions so as to more securely and positively lock the ball portions in ice place; and still further, to provide in a universal tube bending mandrel for a selectively weakened section at the point of connection between the rigid and flexible sections which will selectively rupture in the event of excessive loading so as to remove undue strain or loading from the more expensive parts comprising the flexible mandrel sections.

It is an additional object of the present invention to provide in a universal tube bending mandrel for flexible mandrel sections having ball and socket connecting links of one-piece construction being so constructed and arranged that ball spacing is held at a minimum in order to provide for the maximum number of balls to support the tube throughout the entire bend but without in any way restricting the flexibility of the mandrel sections.

The above and other objects, advantages and features of the present invention will become more readily understood and appreciated from a consideration of the following detailed description when taken together with the accompanying drawings, in which:

FIGURE 1 is a view, partially in section, of a preferred form of flexible tube bending mandrel, in accordance with the present invention;

FIGURE 2 is an enlarged sectional view of the preferred form of mandrel shown in FIGURE 1 and being modified to illustrate the use of a ball detent assembly;

FIGURE 3 is a view in section of a modified form of flexible mandrel section; and

FIGURE 4 is a view in section of another modified form of flexible mandrel section in accordance with the present invention.

Referring in more detail to the drawings, a preferred form of invention is shown in FIGURES 1 and 2 in which a universal tube bending mandrel or tool 10 is broadly comprised of a straight section 11 and a series of flexible mandrel sections 12. Here the straight section 11 consists of an elongated rod 14 provided with an axial bore 15 and an inner bore 16 of reduced diameter which communicates with an enlarged open recess 18 at the leading end of the rod. An insert 20 is positioned within the recess 18 to establish connection of the flexible mandrel sections to the straight section 11, and for this purpose the insert is provided with a socket 22 in facing relation to the flexible mandrel sections. A threaded opening 23 at the opposite end of the insert receives the threaded end of a cap screw 24 which is inserted through the bores 15 and 16 in order to secure the insert 20 in place within the recess 18. It will be noted that the cap screw 24 is selectively weakened by notching the shank as at 25 so that the cap screw will separate under excessive loading and thereby prevent undue strain from being placed on the more flexible mandrel sections.

The socket 22 has an inner closed end 28 which is generally semi-spherical and continuous outwardly into a straight-sided cylindrical wall section 29, the wall portion 29 corresponding in diameter to the maximum diameter of the inner closed end of the socket. At the entrance to the socket, the insert is provided with an inclined or beveled end surface 30 which terminates at the leading end surface 31 of the mandrel rod; also, the outer end surface 31 is beveled slightly as at 32 in order to afford adequate clearance for bending of the first mandrel section in a manner to be described.

Now considering in more detail the construction and arrangement of the flexible mandrel sections, specifically by reference to FIGURE 2, the flexible mandrel sections 12 are comprised of outer ring members 34 being connected in axially spaced, end-to-end relation by means of one-piece combination ball and socket connecting link portions 35. Each ring 34 is relatively thick-walled but of limited length and has an outer rounded or convex periphery 36 and an inner threaded wall section 37 surrounding the central opening through the ring. The trailing end surface 38 of the ring, in facing relation to the leading end of the straight section 11, is somewhat dishshaped or concave as defined by an inwardly inclined peripheral wall surface 39 terminating in an inner fiat wall surface 40. The opposite end 41 of each ring is relatively fiat and is beveled inwardly to define an inner inclined surface 42 terminating at the end of the inner threaded section 37 of the: ring.

Again, each ball and socket connecting link is of one-piece construction and has a cylindrical socket portion 43 at one end and a spherical ball portion 44 at the opposite end being formed symmetrically about a common longitudinal axis. The socket portion 43 is provided with a threaded, external wall surface 45 engageable with the threaded section 37 of the ring and a socket or cavity 46 corresponding in configuration and size to that of the socket 22 for insert 20. Thus, each socket 46 includes an inner closed end 48 of semi-spherical configuration continuing forwardly at its maximum diameter or width into a straight-sided cylindrical wall section 49 and terminating at the entrance in an inclined end surface 50. The external wall 45 of the socket is threaded for a length corresponding to the length of the threaded section 37 on the ring and tapers forwardly as at 52 into an intermediate portion 54 of limited diameter which serves to join the ball and socket portions. In turn, each ball portion 44 is of generally spherical configuration, with a diameter corresponding to that of the socket 46, and at its point of divergence away from the intermediate portion 54 has a fiat undercut peripheral surface portion 55. Each of the ball and socket connecting links is of corresponding size so that the ball of each link will be in ciose'fitting complementary relation to the inner closed end of the socket of each next link when inserted therein. In order to lock or retain each ball within the next socket portion, a peripheral groove is formed in the cylindrical wall section 49 of each socket at a location immediately behind the ball for placement of a releasable or locking retention member here defined by a circular locking wire 62. The location of the groove 60 behind the ball is at a point such that the clearance between the wall of the socket and the surface of the ball is equal to the thickness of the wire projecting inwardly from the wall of the socket and toward the ball surface when inserted in the groove. Further the depth of the groove is most desirably less than one-half the diameter of the wire so that the greater thickness of the wire will projept inwardly from the wall of the socket for engagement with the ball. The locking wire includes split ends 63 and has some limited resiliency so that upon insertion of the ball in the socket, the ends of the wire can be opened slightly to pass over the intermediate portion 54 then the wire can be contracted inwardly a sufficient extent for movement along the wall of the socket into alignment with the groove 60 at which point it will spring into place within the groove. By virtue of the relationship established between the locking wire and ball, the ball is held firmly against axial shifting or movement but with complete freedom of rotation and rolling movement within the socket so as to permit fiexing of the mandrel sections into the desired curvature.

In assembly, it will be seen that each of the mandrel sections consisting of an outer ring and inner connecting link can be pre-assembled, then in succession the first ball portion is inserted in the socket 22 at the leading end of the straight mandrel section and the locking wire is inserted in the groove behind the ball to releasably lock the ball portion in place within the socket. Thereafter each mandrel section is assembled with the ball portion being locked in the socket portion of the preceding mandrel section until the desired number of mandrel sections are assembled which in length will correspond to the 4 length of the tubing to be bent. In the preferred form, placement of the locking wire is facilitated by the undercut portion 55, since by cooking or flexing the ball portion to one side with the undercut portion aligned opposite a portion of the groove, as in FIGURE 1, an increased clearance area is provided for insertion of the locking wire in the groove whereby the wire may be progressiveiy forced into the groove without interference from the ball by advancing the undercut portion around the groove until the wire is completely inserted. By locking the balls securely in place within the socket portions in the manner described, mandrel sections can be more easily added or subtracted without requirement for stiffeners or dentents positioned between the ball and socket portions to maintain axial alignment between the mandrel sections. Furthermore, since the locking wire is aligned with the undercut portion 55 it will not limit or restrict flexing or bending of the mandrel section so that flexing of the mandrel sections is limited only by engagement between the tapered wall surface 52 and the inclined surfaces at the entrances to the sockets.

In a typical tube bending operation the mandrel is inserted within a tube to be bent and clamped to a suitable die so that as pressure is applied in bending the tube the mandrel will flex to the desired extent while internally supporting the tube against flattening or collapse. Customarily, the straight section of the mandrel may be secured to one end of a hydraulic cylinder rod with the flexible mandrel sections aligned to extend through the section of tubing to be bent. The tubing is then suitably clamped to a forming or bending die which is actuated to force the inserted mandrel sections through the desired bend. The relationship between the ball and socket portions as well as close spacing of the balls will permit a high degree of flexing while maintaining a common center line radius and uniform external diameter throughout the mandrel section. Most important, the balls are held within the inner closed ends of the sockets against shiftin or movement so that the mandrel sections will be of uniform length when in use.

As illustrated in FIGURE 2, a ball detent assembly may be disposed between the ball and closed end of the socket having a bore 76 to receive a compression spring 77, and the detent 78 is biased outwardly by the spring into a shallow depression 79 at the center of the inner closed end of the socket. In assembled relation, the ball detent assembly merely serves to prealign the flexible mandrel sections as they are assembled, but in operation the force of the spring is readily overcome to permit flexing of the mandrel sections into the desired bend.

In the modified form of invention shown in FIGURE 3, each mandrel section 12' has an outer ring 34' in which the innner threaded wall 37 extends from the end surface 3-8 for the greater length of the ring and terminates in an inwardly directed ledge 68 having an inner wall surface 70 at the opposite end of the ring, the wall surface 70 having a peripheral groove 71 for insertion of the locking wire 62. Correspondingly, the socket portion 43' is reduced in length and has an external threaded surface 45' engageable with the inner threaded wall section 37' of the ring; and in turn the inner wall 70 forms an extension or continuation of the cylindrical wall surface 49 of the socket. Thus, the modified form departs from the preferred form of the invention to the extent that the inner wall surface 70 of the ring forms part of the internal wall of the socket and whereby the ring itself will support the locking wire to prevent axial displacement of the ball portion from the socket.

In the modified form of invention shown in FIGURE 4, the inner wall 37 of the ring 34 is threaded inwardly from the end 38" for approximately one-half the length of the ring and terminates in a smooth wall surface 81 including an inwardly directed shoulder or ledge 82. An enlarged circular locking or retention member 84 is provided with an external surface 85 complementary to the inner wall surfaces 81 and 82 together with an inner concave bearing surface 86 of spherical configuration and an inclined end surface 87 forming an inward continuation of the end surface 42" of the ring. The socket portion 44" has a semispherical socket 88 which upon assembly within the ring will abut the inner end of the locking member with the inner bearing surface 86 of the retention member forming a continuation of the spherical contour of the socket for the purpose of retaining the ball 43". In assembly, prior to placement of the socket in the ring, the ball of the next connecting link is inserted through the opposite end of the ring, and retention member 84 is inserted through the one end 38" past the ball into position againse the internal shoulder 82. Due to the limited clearance between the ball and inner surface of the ring, the locking member is formed of semi-circular halves which are successively inserted past the ball and positioned against the internal ledge 82 with the ends 90 of the halves in abutting relation to one another. Thereafter, the socket isthreaded inwardly against the inner end of the retention member 84 so as to lock the ball between the socket 44 and the retention member.

It will be noted in accordance with the forms of invent on herein set forth that the ball and socket connecting links are of one-piece integral construction, and the locking or retention members are specially constructed independently of the links so that each ball portion is inserted into the next socket portion in succession and the locking member then is positioned in place behind the ball portion to effectively retain the ball portion against displacement or shifting within the socket. This greatly facilitates assembly and disassembly of the mandrel sections, particularly in the forms of invention illustrated in FIGURES 1 and 2, since it is necessary only to insert or remove the locking wire; and in all forms of invention the locking member will be in direct contact with the ball portion to minimize end play or shifting of the ball with respect to the socket, as well as to afford closer spacing between the ball portions and greatly simplify manufacture, assembly and use of the entire mandrel assembly. Furthermore, where necessary or desired, the insert 20 may be positioned within the recess '18 to project outwardly beyond the leading end 13 either by increasing the length of the insert or by posttioning shims between the inner end of the insert and the end of the recess.

Although the invention has beeen described with reference to preferred and alternate forms thereof, it will be appreciated that various modifications and changes may be made without departing from the spirit and scope of the present invention as set forth in the accompanying claims.

What is claimed is:

1. A tube bending mandrel comprising a series of flexibly interconnected mandrel sections arranged in end-toend relation, each mandrel section having an outer r ng portion, an inner concentric hemispherical socket portion and a cylindrical wall surface forming an extension of said socket portion, a generally spherical 'ball portion projecting from one end of the ring for insertion in a socket portion of each next mandrel section in succession, an annular, releasable retention member having split end portions, said retention member being sized for insertion in a peripheral groove in the cylindrical wall surface at the entrance to each socket and behind the spherical ball portion inserted in each socket to retain each spherical ball portion against axial movement and release from the socket portion while permitting freedom of rotative and pivotal movement of each spherical ball portion with respect to the ring and socket portion within which it is secured.

2. A tube bending mandrel according to claim 1, said releasable retention member being defined by a circular wire being inserted in the peripheral groove at the entrance to each socket portion behind said ball portion.

3. In a tube bending mandrel according to claim 2, said ball portion having a leading end insertable in said socket portion and a trailing end surface provided with an undercut portion which upon tilting of said ball portion with respect to the longitudinal axis of said ring is movable into alignment with the peripheral groove in each socket to provide an increased clearance for insertion of said wire in the groove.

4. A tube bending mandrel according to claim 1, said releasable retention member being characterized by having an inner concave bearing surface, said retention memher being fixed in position behind said ball portion with the inner concave bearing surface forming a continuation of the spherical contour of said socket portion.

5. A tube bending mandrel comprising in combination a straight mandrel section and a series of flexibly interconnected mandrel sections disposed in end-to-end relation, each of said mandrel sections being defined by an outer ring member and an inner concentric connecting link, each connecting link including a socket portion at one end being positioned within said outer ring and a spherical ball portion at the opposite end projecting axially from one end of said ring, each scoket portion having a semi-spherical wall surface at its inner closed end with a cylindrical wall surface forming an extension of each socket portion and corresponding in diameter to that of said ball portion, and a circular locking member being insertable behind said ball portion in fixed relation in a peripheral groove in the cylindrical wall surface at the entrance to each socket portion to contact the outer peripheral surface of said ball portion when said ball portion is disposed against the inner closed end of the socket whereby to retain said ball portion against axial movement while permitting freedom of rotational and pivotal movement of the ball portion with respect to the ring and socket portion within which it is secured.

6. A tube bending mandrel according to claim 5, each socket portion having an externally threaded wall surface engageable with an internally threaded wall surface on the outer ring of each mandrel section and each ring projecting inwardly from the end of said threaded wall section to terminate in a cylindrical wall surface forming an extension of each socket portion for insertion of each ball portion in the inner closed end of each socket portion, and said locking member being defined by a circular wire inserted in a peripheral groove in the cylindrical wall surface, said wire being dimensioned to project inwardly from the cylindrical Wall surface to contact the peripheral surface of said ball portion when said ball portion is disposed against the inner closed end of the socket portion.

7. A tube bending mandrel according to claim 5, said socket portion having an externally threaded Wall surface engageable with an internally threaded wall section on the inner surface of said ring, and said locking member hav ing an external surface complementary to the inner surface of said ring at one end of the internally threaded wall section, and an inner concave bearing surface on said locking member forming a spherical continuation of the inner closed end of said socket portion for retention of the ball portion therebetween.

8. A tube bending mandrel comprising in combination a straight mandrel section including a socket portion at one end and a series of flexibly interconnected mandrel sections disposed in end-to-end relation with respect to one another and with respect to the end of said straight mandrel sections, each of said flexibly interconnected mandrel sections including an outer ring member and an inner concentric connecting link, each connecting link including a socket portion at one end being positioned within said outer ring and a one-piece spherical ball portion at the opposite end projecting outwardly from one end of said ring, each socket portion having a semispherical wall surface at its inner closed end corresponding in diameter to that of said ball portion and a straightsided cylindrical wall surface of a diameter corresponding to the maximum diameter of the inner closed end of said socket portion, and a circular locking wire having split end portions, said wire being inserted in fixed relation in a peripheral groove on the straight-sided wall surface of the socket behind said ball portion, said locking wire being dimensioned to project inwardly from the Wall of the socket into contact with the peripheral surface of said ball portion when said ball portion is disposed within the inner closed end of the socket.

9. A tube bending mandrel according to claim 8 wherein said locking wire is circular in cross-section and is of a diameter greater than that of the diameter of the groove in which it is positioned.

10. A tube bending mandrel according to claim 8, said straight mandrel section including a recess at one end for insertion of the socket portion therein, and an elongated connecting member disposed for extension through an axial bore in said straight mandrel section into connected relation to the socket portion, said connecting member being selectively weakened to separate under excessive strain imposed on said mandrel sections to release the socket portions from the recess.

References Cited UNITED STATES PATENTS 2,971,556 2/1961 Armstrong et al 72466 3,286,503 11/1966 Garrett 72-466 CHARLES W. LANHAM, Primary Examiner E. SUTTON, Assistant Examiner 

